1. Field of the Invention
The present invention relates to an inverter circuit, and more particularly, to an inverter circuit for a backlight of a liquid crystal display (“LCD”).
2. Description of the Related Art
Generally, LCDs have low driving voltage and low power consumption and are lightweight and slim. Because of these advantages, LCDs are widely used as display devices in personal computer (“PC”) monitors, television (“TV”) monitors, and so on. Recently, there is an increasing demand for large-sized LCDs.
The LCD includes a backlight and a liquid crystal display unit disposed in front of the backlight. The backlight supplies light to a liquid crystal panel, and the liquid crystal display unit displays an image by using the light supplied from the backlight.
The backlight includes a reflection plate, a light source, and an optical sheet. When a current is applied to the light source, the light source supplies the light to the display unit.
A cold cathode fluorescent lamp (“CCFL”) has been used as the backlight of the LCD. The CCFL has two terminals and emits light when high alternating-current (“AC”) voltages are applied to the two terminals. As being one of many home appliances used, the LCD is supplied with an external AC of 110-120 volts. The LCD transforms the external AC voltage into a direct-current (“DC”) voltage and pulse-drives a primary side of an inverter transformer using the DC voltage. Also, the LCD drives a CCFL using an AC voltage boosted at a secondary side of the inverter transformer. An inverter circuit is used to pulse-drive the primary side of the inverter transformer.
In the backlight of the LCD, a single inverter transformer turns on a single CCFL. As a screen size of the LCD becomes larger, a high voltage from the inverter transformer is applied to a plurality of CCFLs connected in parallel.
FIG. 9 is a schematic circuit diagram of a conventional inverter circuit for a plurality of CCFLs connected in parallel by applying a high voltage from an inverter transformer. Reference numerals 1000, 1001 and 1002-1 to 1002-n represent an inverter transformer, a resistor and CCFLs, respectively. An AC voltage boosted at a secondary side of the inverter transformer 1000 is applied to the CCFLs 1002-1 to 1002-n. The resistor 1001 is a resistor that detects a current flowing through the CCFLs 1002-1 to 1002-n. A reference numeral 1004 represents a balance circuit that has balance transformers 1003-1 to 1003-n. The balance circuit 1004 is connected in series to the CCFLs 1002-1 to 1002-n. 
The primary sides of the balance transformers 1003-1 to 1003-n are connected in series between the CCFLs 1002-1 to 1002-n and a ground GND, respectively. The secondary sides of the balance transformers 1003-1 to 1003-n form a closed loop. Therefore, a current is flowing through the closed loop commonly flows through the secondary sides of the balance transformers 1003-1 to 1003-n. Currents iL1, iL2, . . . iLn flowing through the respective CCFLs 1002-1 to 1002-n connected to the primary sides of the balance transformers 1003-1 to 1003-n maintain the balance.
However, the conventional inverter circuit of FIG. 9 requires as many balance transformers as there are CCFLs. To meet the demand for the large-sized backlight for use in the large-sized LCD, the number of the CCFLs has to correspondingly increase. However, the increase in the number of the CCFLs causing the corresponding increase in the number of the balance transformers increases the manufacturing cost. Further, to make the large-sized backlight, a balance circuit board for the balance circuit also has to be large-sized, thus increasing the manufacturing cost.